In a telecommunications network in which a mobile handset is capable of communicating in both an IP domain and a non-IP domain, the handoff of an existing communications session between the mobile handset and a fixed user is facilitated by a handoff controller implemented in a service control point. The handoff controller implements different handoff methods depending on the status of the fixed user and the transition of the mobile user. Additionally 802.21 Media Independent Handover Function in conjunction with SIP is used to facilitate handover between IP and Non-IP points in the system.